1. Field of the Invention
The present invention relates to a cap attachment structure for an accumulator of the type having a piston slidably fitted in an outer case.
2. Description of the Relevant Art
Accumulators are widely used as energy sources in a variety of fluid pressure operated devices. The accumulators are largely classified into bladder-type accumulators and piston-type accumulators.
Japanese Patent Publication No. 48-30929 published Sep. 25, 1973 discloses a piston-type accumulator. The disclosed piston-type accumulator comprises a cylindrical accumulator casing and a piston slidably fitted therein, the piston dividing the interior space of the cylindrical accumulator casing into a gas chamber and a working fluid chamber. Caps are fitted and threaded over the respective opposite ends of the cylindrical accumulator casing.
U.S. Pat. Nos. 3,494,378 and 4,793,381 show bladder-type accumulators. According to the former U.S. patent, a cap on the fluid chamber side is either welded to or staked on and welded to an end of an accumulator casing. According to the latter U.S. patent, caps are inserted and threaded in respective opposite ends of an accumulator casing.
With the accumulator disclosed in the Japanese Patent Publication No. 48-30929, the caps may possibly be loosened or dislodged due to vibration or the like either after the accumulator components are manufactured and before the accumulator is assembled or after the accumulator is assembled. The same problem arises with the accumulator disclosed in U.S. Pat. No. 4,793,381.
The caps are prevented from being loosened or detached if they are welded as disclosed in U.S. Pat. No. 3,494,378. However, the heat generated when the caps are welded to the accumulator casing is liable to adversely affect rubber components of the accumulator, such as packings, seals, or the like. The process of manufacturing the disclosed accumulator is complex because the caps are required to be cooled when welded.
The accumulator casing of the piston-type accumulator tends to be broken if a large pressure buildup is developed in the accumulator casing. This also holds true for the accumulators shown in the above U.S. patents. Another problem with the piston-type accumulator is that the piston may pop out of the casing under unduly high pressure before or at the same time the accumulator casing is broken.
The present invention has been made in an effort to effectively solve the aforesaid problems of the conventional accumulators.